U.S. patent application number 12/181361 was filed with the patent office on 2010-02-04 for apparatus and method to improve wlan performance in a dual wlan modality environment.
This patent application is currently assigned to SONY ERICSSON MOBILE COMMUNICATIONS AB. Invention is credited to Jacobus C. HAARTSEN, Huaiyuan WANG.
Application Number | 20100029325 12/181361 |
Document ID | / |
Family ID | 40671264 |
Filed Date | 2010-02-04 |
United States Patent
Application |
20100029325 |
Kind Code |
A1 |
WANG; Huaiyuan ; et
al. |
February 4, 2010 |
APPARATUS AND METHOD TO IMPROVE WLAN PERFORMANCE IN A DUAL WLAN
MODALITY ENVIRONMENT
Abstract
A portable communication device including a first wireless
transceiver operable under a first communication protocol for
transmitting and receiving signals and a second wireless
transceiver operable under a second communication protocol for
transmitting and receiving signals and a method for controlling
transmission of signals from an access point to the first wireless
transceiver by limiting transmission of information from the
associated access point to the first wireless transceiver to time
slots or sub-frames associated with the second wireless transceiver
in which the second wireless transceiver does not transmit.
Inventors: |
WANG; Huaiyuan; (Cary,
NC) ; HAARTSEN; Jacobus C.; (Hardenberg, NL) |
Correspondence
Address: |
WARREN A. SKLAR (SOER);RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, 19TH FLOOR
CLEVELAND
OH
44115
US
|
Assignee: |
SONY ERICSSON MOBILE COMMUNICATIONS
AB
Lund
SE
|
Family ID: |
40671264 |
Appl. No.: |
12/181361 |
Filed: |
July 29, 2008 |
Current U.S.
Class: |
455/553.1 ;
370/338 |
Current CPC
Class: |
H04W 84/12 20130101;
H04W 72/1289 20130101; H04W 72/1215 20130101; H04W 88/06
20130101 |
Class at
Publication: |
455/553.1 ;
370/338 |
International
Class: |
H04B 1/38 20060101
H04B001/38 |
Claims
1. A portable communication device comprising: a first wireless
transceiver operable under a first communication protocol for
transmitting and receiving signals; a second wireless transceiver
operable under a second communication protocol for transmitting and
receiving signals; a controller coupled to the first transceiver
and the second transceiver, wherein the controller coordinates
transmission and reception of the first transceiver and the second
transceiver by limiting transmission of information from the
associated access point to the first wireless transceiver to time
slots or sub-frames associated with the second wireless transceiver
in which the second wireless transceiver does not transmit.
2. The portable communication device of claim 1, wherein a signal
is transmitted from the first transceiver to an associated access
point during at least a portion of a transmit time slot or uplink
sub-frame associated with the second transceiver such that an
acknowledgment signal will be received from the associated access
point at the first transceiver during a receive time slot or
downlink sub-frame associated with the second transceiver.
3. The portable communication device of claim 2, wherein the signal
transmitted from the first transceiver to the associated access
point is an uplink trigger frame.
4. The portable communication device of claim 3, wherein the uplink
trigger frame includes a voice over Internet Protocol (VoIP)
payload, a non-real-time payload, or a null payload.
5. The portable communication device of claim 1, wherein the first
communication protocol is a wireless local area network
protocol.
6. The portable communication device of claim 5, wherein the
wireless local area network protocol is an IEEE 802.11
communication protocol.
7. The portable communication device of claim 1, wherein the second
communication protocol is a Bluetooth compatible communication
protocol or a wireless wide area network compatible communication
protocol.
8. The portable communication device of claim 1, wherein the first
transceiver is operable at a first frequency range and the second
transceiver is operable at a second frequency range, wherein at
least a portion of the first frequency range and the second
frequency range overlap and/or are adjacent with insufficient
spectrum separation.
9. The portable communication device of claim 1, wherein the device
is in a power saving mode when initializing transmission of the
signal from the first transceiver to the associated access
point.
10. A method of coordinating wireless communications in a portable
communication device having a first radio system and a second radio
system, the method comprising: providing a portable communication
device having a first wireless transceiver operable under a first
communication protocol for transmitting and receiving signals at a
first frequency range and a second wireless transceiver operable
under a second communication protocol for transmitting and
receiving signals at a second frequency range, wherein at least a
portion of the first frequency range and the second frequency range
overlap and/or are adjacent with insufficient spectrum separation;
controlling transmission of signals from the associated access
point to the first wireless transceiver by limiting transmission of
information from the associated access point to the first wireless
transceiver to receive time slots or downlink sub-frames associated
with the second wireless transceiver in which the second wireless
transceiver does not transmit.
11. The method of claim 10, wherein the step of controlling
transmission of signals from the associated access point to the
first wireless transceiver further includes transmitting a signal
from a first radio system to an associated access point such that a
downlink acknowledgment signal will be received from the associated
access point at the first transceiver during a receive time slot or
downlink sub-frame associated with the second transceiver.
12. The method of claim 11, wherein the signal transmitted from the
first radio system to the associated access point is transmitted
during at least a portion of a transmit time slot or uplink
sub-frame associated with the second radio system.
13. The method of claim 11, wherein the signal transmitted from the
first radio system to the associated access point is transmitted
during at least a portion of an inactive time slot or sub-frame
associated with the second radio system.
14. The method of claim 11, wherein the signal transmitted from the
first radio system to the associated access point is an uplink
trigger frame (UTF).
15. The method of claim 12, wherein the UTF includes a Voice over
Internet Protocol (VoIP) payload.
16. The method of claim 11, wherein the portable communication
device is in a power saving mode when initializing transmission of
the signal from the first radio system to the associated access
point.
17. The method of claim 11, wherein the step of controlling
transmission of signals from the associated access point to the
portable communication devices includes determining a transmit
opportunity end point by calculating: a minimum value of either
t.sub.RX-SIFS-T.sub.UTF-T.sub.ACK-SIFS or t.sub.RX-D.sub.TX, where
t.sub.RX is the starting time of a next Bluetooth RX slot or
downlink sub-frame, T.sub.ACK is the transmission time of the
uplink acknowledgement signal at a most robust rate, T.sub.UTF is a
duration of the UTF frame, and D.sub.TX is the duration of the
Bluetooth TX slot or uplink sub-frame, and SIFS is the duration of
a short interframe spacing.
18. The method of claim 12, wherein the step of controlling
transmission of signals from the associated access point to the
portable communication devices includes the associated access point
determining an amount of time to download complete downlink
transmission to the portable communication device, wherein the
amount of time is equal to the transmit opportunity as set forth in
the UTF frame minus turnaround delay minus downlink ACK transmit
time minus a SIFS duration time minus a duration time field as set
in the signal.
19. A computer program stored on a machine readable medium, the
program being suitable for coordinating wireless communications in
a portable communication device having a first radio system and a
second radio system, wherein when the program is loaded in memory
in the portable communication device and executed causes the
portable communication device to control transmission of signals
from an associated access point to the first wireless radio system
by limiting transmission of information from the associated access
point to the first wireless transceiver to one or more time slots
or sub-frames associated with the second wireless transceiver in
which the second wireless transceiver does not transmit.
20. The computer program of claim 19, wherein the first radio
system is operating an IEEE 802.11 communication protocol and the
second radio system is operating a Bluetooth compatible
communication protocol or a wireless wide area network compatible
communication protocol.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus and method to
improve wireless local area network (WLAN) communications for
communication devices that utilize dual WLAN communication
modalities (e.g., Bluetooth and IEEE 802.11, Wireless Wide Area
Network and IEE802.11).
DESCRIPTION OF THE RELATED ART
[0002] Electronic equipment, such as portable communication
devices, have evolved from voice-only electronic devices to
multi-functional electronic devices. For example, portable
communication devices, such as mobile telephones, may now function
as electronic organizers, digital cameras, audio applications
(e.g., MP3 players), video applications (e.g., video players),
video game terminals, etc. Moreover, portable communication devices
are not only used for voice communications, but they also are used
in a variety of other forms (e.g., in instant messaging
applications, sharing photographs, gaining access to information on
the Internet, etc).
[0003] One driver behind the increased capabilities of electronic
equipment is the proliferation of multi-radio design and
implementation in wireless mobile devices. In addition to wide area
network (WAN) technologies (e.g., UMTS/HSPA/LTE, CDMA/EV-DO/UMB,
and WiMAX), peripheral technologies such as wireless local area
network (WLAN) (e.g., IEEE 802.11) and Bluetooth have become more
and more integral in future mobile devices.
[0004] Multi-radio coexistence has become an increasingly important
issue as more and more heterogeneous radios, which operate in
adjacent or overlapping frequency bands, are packed into a
space-confined portable communication device platform. In such
cases, in-band and out-of-band interference may cause the receiver
of one radio to be blocked by the simultaneous transmission from
another co-locating radio due to insufficient signal isolation.
[0005] Coexistence has been a long standing problem between WLAN
(IEEE 802.11 b/g/n) and Bluetooth as both operate in the
2.4.about.2.5 GHz ISM band. Similar coexistence challenges also
exist between WLAN (IEEE 802.11 b/g/n) operating in the
2.4.about.2.5 GHz ISM band and WWAN (IEEE 802.16e, IEEE 802.16m and
3GPP TDD) operating in the adjacent 2.5.about.2.69 GHz IMT-2000 3 G
Extension band or the 2.3.about.2.4 GHz band. The problems may be
summarized in two usage scenarios: 1) signals transmitted by the
WLAN transmitter may interfere with reception of Bluetooth or WWAN
signals by a Bluetooth or WWAN receiver; and 2) signals transmitted
by the Bluetooth or WWAN transmitter may interfere with reception
of WLAN signals by the WLAN receiver.
[0006] In the WLAN and Bluetooth coexistence scenario, the first
problem has been somewhat mitigated by the so-called PTA (Packet
Traffic Arbitration) mechanism defined in IEEE 802.15.2 and
implemented by most vendors in combination with WLAN-Bluetooth
integrated circuits and improved signaling between the two radios
modules. In short, the IEEE 802.15.2 PTA solution causes WLAN
transmission to be blocked when Bluetooth is receiving higher
priority (voice) packets. This solution minimizes the impact on
signals received by the Bluetooth transceiver, which originate from
the WLAN transceiver. With respect to the WLAN and WWAN coexistence
scenario, there has not been any industry wide solution for such
scenario.
SUMMARY
[0007] The second problem identified above is more subtle and more
difficult to solve for at least two reasons. First, the WLAN access
point is not aware of the Bluetooth or WWAN transmission and
reception schedule. Second, there is no synchronization between the
WLAN access point and the Bluetooth and/or WWAN transceiver of the
portable communication device. A need exists for a method and an
electronic device having a WLAN transceiver and a Bluetooth and/or
WWAN transceiver to provide appropriate signaling to prevent the
WLAN access point from transmitting to the electronic device during
each of the Bluetooth transmit slots and/or WWAN TDD uplink
sub-frames.
[0008] Aspects of the present invention are applicable to any
multi-radio coexistence wherein the isolation between radios, which
may operate in overlapping or non-overlapping bands, is not large
enough, meaning that the transmit spectrum of one radio interferes
with the reception of another radio. For example, the 2.5 GHz
extension band is not completely adjacent to the 2.4 GHz band. The
2.4 GHz band ends at 2483.5 MHz, whereas the 2.5 GHz band starts at
2500 MHz. These bands are deemed to be "adjacent" in the context of
the present invention since the isolation between radios operating
in these frequencies are likely to interfere (i.e., the transmit
spectrum of one radio is likely to interfere with the reception of
another radio).
[0009] One aspect of the present invention relates to a coexistence
solution that makes use of the fact that when the WLAN transceiver
and the Bluetooth or the WWAN transceiver are both transmitting,
interference between the signals can be eliminated and/or
substantially reduced. Likewise, when the WLAN transceiver and the
Bluetooth or the WWAN transceiver are both receiving, interference
between the signals can be eliminated and/or substantially
reduced.
[0010] One aspect of the present invention relates to a portable
communication device including: a first wireless transceiver
operable under a first communication protocol for transmitting and
receiving signals; a second wireless transceiver operable under a
second communication protocol for transmitting and receiving
signals; a controller coupled to the first transceiver and the
second transceiver, wherein the controller coordinates transmission
and reception of the first transceiver and the second transceiver
by limiting transmission of information from the associated access
point to the first wireless transceiver to time slots or sub-frames
associated with the second wireless transceiver in which the second
wireless transceiver does not transmit.
[0011] Another aspect of the invention relates to a signal being
transmitted from the first transceiver to an associated access
point during at least a portion of a transmit time slot or uplink
sub-frame associated with the second transceiver such that an
acknowledgment signal will be received from the associated access
point at the first transceiver during a receive time slot or
downlink sub-frame associated with the second transceiver.
[0012] Another aspect of the invention relates to the signal
transmitted from the first transceiver to the associated access
point is an uplink trigger frame.
[0013] Another aspect of the invention relates to the uplink
trigger frame (UTF) including a voice over Internet Protocol (VoIP)
payload, a non-real-time payload, or a null payload.
[0014] Another aspect of the invention relates to the first
communication protocol is a wireless local area network
protocol.
[0015] Another aspect of the invention relates to the wireless
local area network protocol being an IEEE 802.11 communication
protocol.
[0016] Another aspect of the invention relates to the second
communication protocol being a Bluetooth compatible communication
protocol or a wireless wide area network compatible communication
protocol.
[0017] Another aspect of the invention relates to the first
transceiver being operable at a first frequency range and the
second transceiver is operable at a second frequency range, wherein
at least a portion of the first frequency range and the second
frequency range overlap and/or are adjacent.
[0018] Another aspect of the invention relates to the device being
power saving mode prior to initializing transmission of the signal
in a sleep mode when transmitting the signal from the first
transceiver to the associated access point.
[0019] One aspect of the invention relates to a method of
coordinating wireless communications in a portable communication
device having a first radio system and a second radio system, the
method including: providing a portable communication device having
a first wireless transceiver operable under a first communication
protocol for transmitting and receiving signals at a first
frequency range and a second wireless transceiver operable under a
second communication protocol for transmitting and receiving
signals at a second frequency range, wherein at least a portion of
the first frequency range and the second frequency range overlap
and/or are adjacent; controlling transmission of signals from the
associated access point to the first wireless transceiver by
limiting transmission of information from the associated access
point to the first wireless transceiver to receive time slots or
downlink sub-frames associated with the second wireless transceiver
in which the second wireless transceiver does not transmit.
[0020] Another aspect of the invention relates to the step of
controlling transmission of signals from the associated access
point to the first wireless transceiver further including
transmitting a signal from a first radio system to an associated
access point such that a down link acknowledgment signal will be
received from the associated access point at the first transceiver
during a receive time slot or downlink sub-frame associated with
the second transceiver.
[0021] Another aspect of the invention relates to the signal being
transmitted from the first radio system to the associated access
point is transmitted during at least a portion of a transmit time
slot or uplink sub-frame associated with the second radio
system.
[0022] Another aspect of the invention relates to the signal
transmitted from the first radio system to the associated access
point is transmitted during at least a portion of an inactive time
slot or sub-frame associated with the second radio system.
[0023] Another aspect of the invention relates to the signal being
transmitted from the first radio system to the associated access
point is an uplink trigger frame (UTF).
[0024] Another aspect of the invention relates to the UTF includes
a Voice over Internet Protocol (VoIP) payload.
[0025] Another aspect of the invention relates to the portable
communication device being in a power saving mode when initializing
transmission of the signal from the first radio system to the
associated access point.
[0026] Another aspect of the invention relates to controlling
transmission of signals from the associated access point to the
portable communication devices including determining a transmit
opportunity end point by calculating a minimum value of either
t.sub.RX-SIFS-T.sub.UTF-T.sub.ACK-SIFS or t.sub.RX-D.sub.TX, where
t.sub.RX is the starting time of the next RX slot or downlink
sub-frame, T.sub.ACK is the transmission time of the uplink ACK at
the most robust data rate, T.sub.UTF is the duration of the UTF
packet, D.sub.TX is the duration of the TX slot or uplink
sub-frame, and SIFS is the duration of a short interframe
spacing.
[0027] Another aspect of the invention relates to controlling
transmission of signals from the associated access point to the
portable communication devices including the associated access
point determining an amount of time it has to downlink transmission
to the portable communication device, wherein the amount of time is
equal to the transmit opportunity, which is indicated by the
portable communication device in UTF, minus access point turnaround
delay minus downlink ACK transmit time minus a SIFS duration time
minus a duration time field as set in the UTF.
[0028] One aspect of the invention relates to a computer program
stored on a machine readable medium, the program being suitable for
coordinating wireless communications in a portable communication
device having a first radio system and a second radio system,
wherein when the program is loaded in memory in the portable
communication device and executed causes the portable communication
device to control transmission of signals from an associated access
point to the first wireless radio system by limiting transmission
of information from the associated access point to the first
wireless transceiver to one or more time slots or downlink
sub-frames associated with the second wireless transceiver in which
the second wireless transceiver does not transmit.
[0029] Another aspect of the invention relates to the first radio
system operating an IEEE 802.11 communication protocol and the
second radio system operating a Bluetooth compatible communication
protocol or a wireless wide area network compatible communication
protocol.
[0030] Another aspect of the invention relates to the signal
transmitted from the first radio system to the associated access
point being transmitted during at least a portion of a transmit
time slot and/or an inactive time slot and/or uplink sub-frame
associated with the second radio system.
[0031] Another aspect of the invention relates to the signal
transmitted from the first radio system to the associated access
point being an uplink data frame (UDF).
[0032] Other systems, devices, methods, features, and advantages of
the present invention will be or become apparent to one having
ordinary skill in the art upon examination of the following
drawings and detailed description. It is intended that all such
additional systems, methods, features, and advantages be included
within this description, be within the scope of the present
invention, and be protected by the accompanying claims.
[0033] It should be emphasized that the term "comprise/comprising"
when used in this specification is taken to specify the presence of
stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features,
integers, steps, components or groups thereof."
[0034] The term "portable communication device", includes all
equipment such as mobile telephones, pagers, communicators, i.e.,
electronic organizers, personal digital assistants (PDA's),
portable communication apparatus, smart phones or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The foregoing and other embodiments of the invention are
hereinafter discussed with reference to the drawings. The
components in the drawings are not necessarily to scale, emphasis
instead being placed upon clearly illustrating the principles of
the present invention. Likewise, elements and features depicted in
one drawing may be combined with elements and features depicted in
additional drawings. Moreover, in the drawings, like reference
numerals designate corresponding parts throughout the several
views.
[0036] FIG. 1 is an exemplary block diagram of a system in
accordance with aspects of the present invention.
[0037] FIG. 2 is an exemplary Bluetooth timing sequence.
[0038] FIG. 3 is an exemplary timing sequence between a Bluetooth
master and a WLAN access point.
[0039] FIG. 4 is an exemplary timing sequence of an unscheduled
automatic power savings delivery (U-APSD) mechanism.
[0040] FIG. 5 is an exemplary block diagram of a portable
communication device and an accessory in accordance with aspects of
the present invention.
[0041] FIGS. 6 and 7 are exemplary timing sequences for Bluetooth
and WLAN coexistence solution in accordance with aspects of the
present invention.
[0042] FIG. 8 is an exemplary time division duplex (TDD) frame
structure of a WWAN system.
[0043] FIG. 9 is an exemplary timing sequence for a WWAN TDD system
and WLAN coexistence solution in accordance with aspects of the
present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0044] Aspects of the present invention relate to a device and
method to improve wireless local area network (WLAN) communications
for communication devices that utilize dual WLAN communication
modalities (e.g., Bluetooth and IEEE 802.11 or WWAN and IEEE
802.11). In particular, a coexistence solution is provided that
makes use of the fact that when the WLAN transceiver and the
Bluetooth/WWAN transceiver are both transmitting, interference
between the two signals can be eliminated and/or substantially
reduced. Likewise, when the WLAN transceiver and the Bluetooth/WWAN
transceiver are both receiving, interference between the two
signals can be eliminated and/or substantially reduced.
[0045] In one embodiment, a portable communication device includes
a first wireless transceiver operable under a first communication
protocol for transmitting and receiving signals and a second
wireless transceiver operable under a second communication protocol
for transmitting and receiving signals and a method for controlling
transmission of signals from an access point to the first wireless
transceiver by limiting transmission of information from the
associated access point to the first wireless transceiver to time
slots or sub-frames associated with the second wireless transceiver
that are either a receive time slot or an inactive time slot or a
downlink sub-frame. In other words, transmissions from the WLAN
access point are limited to time slots or sub-frames when the
second wireless transceiver (e.g., Bluetooth, WWAN, etc.) does not
transmit.
[0046] One issue facing wireless system designers when considering
voice and other time-sensitive services over a WLAN connection,
such as one described by the IEEE 802.11 specification, is the
power consumption of handheld devices. For example, in order to
deliver competitive talk time and standby time, as compared to
digital cordless or cellular devices, power conservation during
voice calls become necessary. Several organizations have proposed
power-efficient operation via transmit power control and physical
layer rate adaptation for systems that rely on a centrally
controlled contention-free channel access scheme. However, such
approaches can be complex to implement and may not provide the
power savings required to justify the complexity.
[0047] The 802.11 standard defines procedures that can be used to
implement power management in a handheld device during periods of
inactivity. The most commonly used power saving mechanisms are
legacy power saving mode and Unscheduled Automatic Power Saving
Delivery (U-APSD) mode. A portable communication device may combine
these power saving mechanisms in various manners to support power
management for different applications.
[0048] The 802.11 power saving operation involves alternating
Active State and Sleep State:
[0049] Active State: There are generally two reasons for the
portable communication device to wake up, namely to transmit
pending data or to retrieve buffered data from the access point
serving the portable communication device. Waking up to transmit
data is a straightforward operation, driven by the portable
communication device. The decision to wake up and receive data is
also made by the portable communication device after monitoring its
pending data bit in a periodic beacon frame transmitted by its
access point. Once the portable communication device decides to
transition from sleep state to active state, it notifies the access
point by sending a PS-Poll frame when operating in legacy power
saving mode or a trigger frame when operating in U-APSD mode.
Following such transmission, the portable communication device
remains active so the access point can send any buffered downlink
frames afterward.
[0050] Sleep State: In legacy power saving mode, portable
communication device transitions from Active State to Sleep State
after receiving and acknowledging one downlink packet. In U-APSD
mode, the portable communication device only switches back to Sleep
State when instructed so by access point via the EOSP (End of
Service Period) flag. The access point needs to buffer all traffic
destined to the portable communication device when it is in Sleep
State.
[0051] An exemplary architecture of a common dual mode WLAN system
10 is depicted in FIG. 1. The system 10 includes a network 12,
consisting of an access point 14 and portable electronic equipment,
such as a data station 16 and a portable communication device 18.
The portable electronic equipment are connected to the access point
via WLAN radio links 20, 22, respectively. The access point 14 may
be coupled to a distribution network, including voice and data
gateways 24, 26 respectively, through a switch 28. The portable
communication device 18 may execute a Voice-over-IP (VoIP)
application, which establishes a peer-to-peer connection with the
voice gateway 24, representing the other end of the voice call, and
which routes voice data to a voice network 30. Data station 16 may
connect to the data gateway 26 via the access network and connect
to, for example, a wide area network 32. The impact of data traffic
on voice quality should be considered. It is assumed that both the
voice and data stations employ a prioritized contention-based
quality of service mechanism. The portable electronic equipment may
also communicate directly to a base station 39, which connects to
wide area network 32 via link 38, through a time division duplex
(TDD) communication link 37 (e.g., 3GPP, 811.16e, etc.)
[0052] The portable communication device 18 may be wirelessly
coupled to an accessory 34. The accessory 34 in the exemplary
embodiment is a rendering device in the form of a headset. The
accessory 34 is shown as an ear mountable speaker and microphone
assembly that exchanges audio data with the portable communication
device 18 over a wireless link 36. One of ordinary skill in the art
will appreciate that any accessory operable to receive signals
discussed herein is deemed to fall within the scope of the present
invention. For example, suitable accessories include headphones,
earphones, speakers, stereos, and the like.
[0053] The wireless link 36 between the portable communication
device 18 and the headset 34 is established using a Bluetooth
compatible protocol, such as in accordance with the Specification
of the Bluetooth System, Covered Core Package version 2.0+EDR,
dated Nov. 4, 2004. Bluetooth specifies communication protocols for
low cost, low power wireless devices that operate over a very small
area, the so-called, personal area network. These wireless devices
may include, for example, telephone headsets, cell phones, Internet
access devices, personal digital assistants, laptop computers, etc.
Typically, the Bluetooth specification seeks to replace a
connecting cable between communicating devices, for example, a
mobile telephone and a headset, with a wireless radio link to
provide greater ease of use by reducing the tangle of wires
frequently associated with personal communication systems. Several
such personal communication devices may be "wirelessly" linked
together by using the Bluetooth specification.
[0054] Because Bluetooth devices operate in the unlicensed 2.4 GHz
radio frequency band, they are subject to radio interference from
other wireless devices operating in the same frequency band. To
avoid radio frequency interference, the Bluetooth specification
divides the 2.4 to 2.5 GHz frequency band into 1 MHz-spaced
channels. Each channel signals data packets at 1 Mb/s, using a
Gaussian Frequency Shift Keying modulation scheme. A Bluetooth
device transmits a modulated data packet to another Bluetooth
device for reception. After a data packet is transmitted and
received, both devices retune their radio to a different 1 MHz
channel, effectively hopping from radio channel to radio channel,
i.e., frequency-hopping spread spectrum (FHSS) modulation, within
the 2.4 to 2.5 GHz frequency band. In this way, Bluetooth devices
use most of the available 2.4 to 2.5 GHz frequency band and if a
particular signal packet transmission/reception is compromised by
interference on one channel, a subsequent retransmission of the
particular signal packet on a different channel may be possible for
eSCO or ACL links.
[0055] Bluetooth devices operate in one of two modes: as a Master
device or a Slave device. The Master device provides a network
clock and determines the frequency hopping sequence. One or more
Slave devices synchronize to the Master's clock and follow the
Master's hopping frequency. Bluetooth is a time division
multiplexed system, where the basic unit of operation is a time
slot of 625 .mu.s. Referring to FIG. 2, the Master device first
transmits to the Slave device during a first time slot of 625 .mu.s
with both devices tuned to the same radio frequency channel. Thus,
the Master device transmits and the Slave device receives during
the first time slot. Following the first time slot, the two devices
retune their radios, or hop, to the next channel in the frequency
hopping sequence for the second time slot. During the second time
slot, the Slave device must respond whether it successfully
understood, or not, the last packet transmitted by the Master
during the first time slot. Thus, the Slave device transmits and
the Master device receives during the second time slot. As a Slave
device must respond to a Master's transmission, communication
between the two devices requires at a minimum two time slots or
1.25 ms. For example, referring to FIG. 2, an exemplary Bluetooth
time sequence is illustrated. The Master 50 outputs a transmit (TX)
time slot 52 that has a duration of 625 .mu.s. The Slave must
respond during the receive (RX) time slot 54, which also has a
duration of 625 .mu.s. When a HV3 packet type is used on a SCO
link, there will be a 2.5 ms inactive period 56 that consists of
four (4) inactive time slots. Thus, voice packets are exchanged
between Master and Slave every 3.75 milliseconds. This pattern
repeats itself as necessary for communication purposes.
[0056] Data packets, when transmitted over networks, are frequently
susceptible to delays by, for example, retransmissions of packets
caused by errors, sequence disorders caused by alternative
transmission pathways, etc. Packet delays do not cause much of a
problem with the transmission of digital data because the digital
data may be retransmitted or re-sequenced by the receiver without
effecting the operation of computer programs using the digital
data. However, packet delays or dropped packets during the
transmission of voice signals can cause unacceptable quality of
service.
[0057] The Bluetooth specification version 1.1 provides a
Synchronous Connection Oriented (SCO) link for voice packets that
is a symmetric link between Master and Slave devices with periodic
exchange of voice packets during reserved time slots. The Master
device will transmit SCO packets to the Slave device at regular
intervals, defined as the SCO interval or T.sub.SCO, which is
counted in time slots. Bandwidth limitations limit the Bluetooth
specification to a maximum of three SCO links. Hence, the widest
possible spacing for an SCO pair of time slots, which are sometimes
called a voice slot, is every third voice slot. Bluetooth
specification version 1.2 provides enhanced SCO links, i.e., eSCO
links, which have a larger voice slot size, based on N*625 .mu.s
time slots, with larger and configurable intervals between voice
slots. These eSCO links can be used for both voice and/or data
applications.
[0058] The IEEE 802.11 specification for WLANs also uses the same
2.4 GHz radio frequency band as Bluetooth devices. Therefore, radio
interference often occurs when Bluetooth and WLAN devices try to
communicate simultaneously over the same radio frequency band.
[0059] For Example, FIG. 3 provides an exemplary illustration of a
common problem that may be experienced by a portable communication
device having a WLAN transceiver and a Bluetooth transceiver. That
is, signals transmitted by the Bluetooth transceiver may interfere
with reception WLAN signals by the WLAN transceiver. In FIG. 3, a
Bluetooth SCO connection with HV3 packet is assumed.
[0060] The Bluetooth master 50 (e.g., a Bluetooth transceiver of a
portable communication device) first transmits to the slave device
(e.g., a mobile telephone accessory, such as a headset) during a
first time slot 52 of 625 .mu.s. During a first RX time slot 54,
the slave device must respond to the master's transmission. Thus,
communication between the two devices requires at a minimum two
time slots or 1.25 ms. As shown in FIG. 2, which also assumes a
Bluetooth SCO connection with HV3 packet type, there is a 2.5 ms
inactive duration 56, which is made of four (4) time slots. As
such, in this exemplary embodiment, a pair of time slots having a
duration of 1.25 ms may be reserved for the BT SCO voice slot. In
this exemplary embodiment, the BT SCO voice slots are repeated
every 3.75 ms.
[0061] In order to avoid WLAN reception from being impacted by
Bluetooth transmission, two requirements are generally needed to be
met. First, the WLAN access point 14 must not transmit to the
portable communication device 18 (e.g., the Bluetooth Master)
during each of the Bluetooth TX slots. Second, the WLAN access
point 14 must have knowledge about Bluetooth inactive period so as
to fully utilize the period to transmit to the portable
communication device 18.
[0062] To meet the first requirement, the portable communication
device 18 (e.g., Bluetooth Master) may transmit a CTS
(Clear-to-Send) message addressed to itself right before the
arrival of the Bluetooth TX slot. In the CTS message, the Duration
field is set to protect the entire Bluetooth TX duration. This
mechanism is able to stop the WLAN access point 14 from
transmitting to the mobile device (Bluetooth Master) while the
portable communication device is transmitting to the Bluetooth
slave (the headset). There are two primary problems associated with
this signaling mechanism: First, by setting the CTS duration to
cover Bluetooth TX slot, it causes channel dead time. That is, no
traffic may be exchanged between the access point 14 and any mobile
stations (including those that do not have Bluetooth connections)
during the CTS duration. Second, it may force an access point 14 to
postpone the WLAN Beacon transmission, which will impact the
overall system performance (such as association and hand-over
functions).
[0063] Thus, the two primary problems generally require that all
WLAN transmission from the portable communication device 18 takes
place between the Bluetooth RX slots, and that all WLAN reception
for the device takes place between the Bluetooth TX slots. Since
the access point 14 is not aware of the gap between consecutive
Bluetooth TX or RX slots, most vendors took an over-kill approach
by mandating higher data rates at both the access point 14 and the
portable communication devices in order to minimize the chances of
interference. For example, as shown in FIG. 3, the access point 14
has to make sure it can transmit the largest possible packet and
receive acknowledgement within the 2.5 ms gap (referred to as
inactive period 56). As shown in FIG. 3, the exemplary packet
exchange sequence 62 includes a medium access delay period 63, a
downlink PLCP protocol data unit (PPDU) 64, short interframe space
(SIFS) 66, and an uplink Acknowledge message 68. The implications
of such approach [assuming: (1) size of the largest PPDU size of
2372 octets-PLCP Preamble (18 octets), PLCP Header (6 octets), Mac
Header (32 octets), MSDU (2312 octets), FCS (4 octets); (2) size of
the ACK packet is 38 octets; (3) SIFS=10 .mu.s; and (4) average
medium access delay of 18 .mu.s] is that the minimum data rate must
be 9 megabits per second and 11 megabits per second (mbps) for
ERP-OFDM/DSSS-OFDM and ERP-PBCC/ERP-CCK communications,
respectively.
[0064] Such approach is equivalent to setting a data rate floor
regardless of channel conditions. In order to maintain high data
rate when link condition is poor, the access point 14 has to either
boost transmit power, apply heavy fragmentation, or resort to
retransmissions, none of which is ideal by most system performance
measures.
[0065] As discussed above, power savings is a primary concern for
portable communication devices. The IEEE 802.11e standard defines a
power saving mechanism known as Unscheduled Automatic Power Saving
Delivery (U-APSD). U-ASPD allows the portable communication device
to take the initiative as to when to contact the access point.
Therefore, more efficient power savings modes can be implemented in
the terminal.
[0066] The following is a brief description of U-APSD. Referring to
FIG. 4, a timing diagram with the packet exchange between the WLAN
access point (AP) 14 and the portable communication device (STA) 18
is illustrated. At block 80, the portable communication device will
content for the medium. At block 82, an uplink trigger frame, which
may be a data frame or a null frame, is transmitted through its
WLAN transceiver to the AP 14. At block 83, the AP sends an ACK in
response to the received the uplink trigger frame. At block 84, the
AP checks if there is buffered traffic for the portable
communication device and prepares for transmission if there is
traffic waiting. This period is known as the "AP Turnaround Time"
and, depending on actual implementations, usually lasts
approximately 100.about.300 .mu.s (the shorter the better from a
power saving standpoint). At block 86, the AP sends a downlink data
frame or a null frame (if there is no buffered traffic) with an
indication whether there is further downlink transmission to
follow. At block 88, the portable communication device sends an ACK
in response to receiving the downlink frame. Blocks 86 and 88 may
be repeated until the AP signals the End-of-Service-Period (EOSP)
in a downlink data or null frame.
[0067] Referring to FIGS. 1 and 5, a portable communication device
assembly 100 is shown in accordance with the present invention. The
illustrated electronic equipment assembly 100 includes portable
communication device 18 and a wirelessly coupled accessory 34
(e.g., a headset). The portable communication device 18 includes a
display 102. The display 102 presents information to a user such as
operating state, time, telephone numbers, contact information,
various navigational menus, etc., which enables the user to utilize
the various features of the portable communication device 18. The
display 102 may also be used to visually display content accessible
by the portable communication device 18 and/or accessory 34 from
one or more remote sources (e.g., a media server, a network, etc.).
The displayed content may include audio and/or video presentations
stored locally in memory 104 of the portable communication device
18 and/or stored remotely from the portable communication device 18
(e.g., on a remote storage device, a media server, remote personal
computer, etc.).
[0068] The audio component may be broadcast to the user with a
speaker 104 of the portable communication device 18. Alternatively,
the audio component may be broadcast to the user with a speaker 106
(FIG. 4) of the accessory 34. For stereo listening, the accessory
34 may include a pair of speakers 106. The accessory 34 generally
receives audio data from the portable communication device 18
through a wireless Bluetooth communication link 108.
[0069] The portable communication device 18 further includes a
keypad 110 that provides for a variety of user input operations.
For example, the keypad 110 may include alphanumeric keys for
allowing entry of alphanumeric information such as telephone
numbers, phone lists, contact information, notes, etc. In addition,
the keypad typically may include special function keys such as a
"call send" key for initiating or answering a call, and a "call
end" key for ending, or "hanging up" a call. Special function keys
may also include menu navigation keys, for example, for navigating
through a menu displayed on the display 102 to select different
telephone functions, profiles, settings, etc., as is conventional.
Other keys associated with the portable communication device 18 may
include a volume key, audio mute key, an on/off power key, a web
browser launch key, a camera key, etc. Keys or key-like
functionality may also be embodied as a touch screen associated
with the display 18.
[0070] The portable communication device 18 includes conventional
call circuitry that enables the portable communication device 18 to
establish a call and/or exchange signals with a called/calling
device, typically another mobile telephone or landline telephone.
However, the called/calling device need not be another telephone,
but may be some other device such as an Internet web server,
content providing server, etc.
[0071] The portable communication device 18 includes a primary
control circuit 112 that is configured to carry out overall control
of the functions and operations of the portable communication
device 18. The control circuit 112 may include a processing device
114, such as a CPU, microcontroller or microprocessor. The
processing device 114 executes code stored in a memory (not shown)
within the control circuit 112 and/or in a separate memory, such as
memory 116, in order to carry out conventional operation of the
portable communication device 18. The memory 116 may be, for
example, a buffer, a flash memory, a hard drive, a removable media,
a volatile memory and/or a non-volatile memory. In addition, the
processing device 114 executes code to carry out various functions
of the portable communication device 18.
[0072] Continuing to refer to FIGS. 1 and 5, the portable
communication device 18 includes an antenna 118 coupled to a radio
circuit 120 (e.g., GSM, 3G, etc). The radio circuit 120 includes a
radio frequency transmitter and receiver for transmitting and
receiving signals via the antenna 118 as is conventional. The
portable communication device 18 further includes a sound signal
processing circuit 122 for processing the audio signal transmitted
by/received from the radio circuit 120. Coupled to the sound
processing circuit 122 are the speaker 104 and a microphone 124
that enable a user to listen and speak via the portable
communication device 18, as is conventional. The radio circuit 120
and sound processing circuit 122 are each coupled to the control
circuit 112 so as to carry out overall voice operations of the
portable communication device 18.
[0073] The portable communication device 18 also includes the
aforementioned display 102 and keypad 110 coupled to the control
circuit 112. The portable communication device 18 further includes
an I/O interface 126. The I/O interface 126 may be in the form of
typical mobile telephone I/O interfaces, such as a multi-element
connector at the base of the portable communication device 18. As
is typical, the I/O interface 126 may be used to couple the
portable communication device 18 to a battery charger to charge a
power supply unit (PSU) 128 within the portable communication
device 18. In addition, or in the alternative, the I/O interface
126 may serve to connect the portable communication device 18 to a
wired personal hands-free adaptor, to a personal computer or other
device via a data cable, etc. The portable communication device 18
may also include a timer 129 for carrying out timing functions.
Such functions may include timing the durations of calls,
generating the content of time and date stamps, etc.
[0074] The portable communication device 18 may include various
built-in accessories, such as a camera 130 for taking digital
pictures. Image files corresponding to the pictures may be stored
in the memory 116 and/or in a removable memory (not shown). In one
embodiment, the portable communication device 18 also may include a
position data receiver (not shown), such as a global positioning
satellite (GPS) receiver, Galileo satellite system receiver or the
like.
[0075] To establish wireless communication with other locally
positioned devices, such as the accessory 34, another portable
communication, a computer, a printer, etc., the portable
communication device 18 may include a local wireless interface
transceiver 140, such as a Bluetooth transceiver for transmitting
and receiving information to and/or from the accessory 34.
[0076] To establish communications with network-based content, the
portable communication device 18 further include a wireless local
area network interface transceiver 150. Preferably, the WLAN
transceiver 150 is compatible with one or more IEEE 802.11
protocols (e.g., 802.11(a), 802.11(b) and/or 802.11(g), etc.) and
allows the portable communication device 18 to acquire a unique
identifier (e.g., MAC and IP addresses) on an associated network
and communicate with one or more devices on the network, assuming
the user has the appropriate privileges and/or has been properly
authenticated.
[0077] To establish communications with network-based content over
WWAN, the portable communication device 18 further include a WWAN
interface transceiver 155. Preferably, the WWAN transceiver 155 is
compatible with one or more time division duplex protocols (e.g.,
(e.g., IEEE 802.16e, WiMAX, 3GPP, etc.) and allows the portable
communication device 18 to be uniquely identified on an associated
network and communicate with one or more devices on the network,
assuming the user has the appropriate privileges and/or has been
properly authenticated to receive bandwidth allocations.
[0078] Local wireless interface transceiver 140 and WLAN
transceiver 150 are illustrated in FIG. 5 as utilizing a common
antenna 149. One of ordinary skill in the art will appreciate that
the local wireless interface transceiver 140 and the WLAN
transceiver 150 may utilize separate antennas. The WWAN transceiver
155 is illustrated using antenna 157 to transmit and receive WWAN
information.
[0079] The portable communication device 18 may be configured to
operate in a wide area communications system (not illustrated). The
system can include one or more servers, media gateways, and/or call
control elements for managing calls placed by and destined to the
portable communication device 18, transmitting network-based
content (e.g., image files, audio files, video files, etc.) to the
portable communication device 18 and carrying out any other control
functions. The wide area network system may communicate with the
portable communication device 18 via a network and a transmission
medium. The transmission medium may include any appropriate device
or assembly, including, for example, a communications tower,
another mobile telephone, a wireless access point, a router, a
satellite, etc. Portions of the network may include wired and/or
wireless transmission pathways.
[0080] The accessory 34 includes a primary control circuit 160 that
is configured to carry out overall control of the functions and
operations of the accessory 34. The control circuit 160 may include
a processing device 162, such as a CPU, microcontroller or
microprocessor. The processing device 162 executes code stored in a
memory (not shown) within the control circuit 160 and/or in a
separate memory, such as memory (not shown), in order to carry out
operation of the accessory 34, as described herein. The memory may
be, for example, a buffer, a flash memory, a hard drive, a
removable media, a volatile memory and/or a non-volatile memory. In
addition, the processing device 162 executes code to carry out
various functions of the accessory 34. Although not shown, the
accessory 34 may include a user interface (e.g., a display,
buttons, keys, etc.).
[0081] The accessory 34 includes a local interface transceiver 170
that is compatible with the local interface transceiver 140 of the
portable communication device 18 to establish a wireless
communications between the accessory 34 and the portable
communication device 18 through a Bluetooth communication link 108,
for example. The local interface transceiver 170 is coupled to the
control circuit 162 to selectively control and process information
and/or data received and/or transmitted by the local interface
transceiver 170 through the antenna 171. Preferably, as discussed
above, the local interface transceiver 170 is Bluetooth compatible.
The wireless interface established between adapters 140 and 170 may
be used to exchange data, such as audio data, commands, control
and/or status information between the portable communication device
18 and the accessory 34. One of ordinary skill in the art will
understand the basic operations of a Bluetooth wireless
communication interface, so the details will not be described here
in detail for the sake of brevity.
[0082] The accessory 34 further includes an audio data processing
device 172 that manages audio data. For example, the audio data
processing device 172 may include an encoder 174 that encodes an
audio signal received from a microphone 176 coupled to the
accessory 34. Encoded audio data may be transmitted to the portable
communication device 18 for use as part of a telephone call.
[0083] In addition, the audio data processing device 172 may
include a decoder 178 and a data buffer 180 to process audio data
received from the portable communication device 18 and/or one or
more devices associated with a network.
[0084] The received audio data may be incoming audio data
associated with a telephone call (including Voice over Internet
Protocol (VoIP). In other situations, the audio data received by
the accessory 34 may be audio (e.g., music, sound, voice, etc.)
derived from an audio file played back by the portable
communication device 18.
[0085] In accordance with the Bluetooth specification, audio data
transmitted from the portable communication device 18 to the
accessory 34 is typically in the form of media packets. Each media
packet may contain a quantity of audio data, such as about 5
milliseconds of audio data. The audio data may be buffered by the
buffer 180 and decoded by the decoder 178 into an audio signal for
delivery to the speaker 106. As will be appreciated, the audio data
may be mono, stereo or surround-sound, or arranged in any other
suitable audio format.
[0086] An exemplary method 200 in accordance with aspects of the
invention is illustrated in FIG. 6. FIG. 6 illustrates an exemplary
timing diagram with the packet exchange between the access point
(AP) 14 and the portable communication device (STA) 18. The method
200 assumes that the portable communication device 18 is in a power
saving mode when initializing transmission of the signal (see
Active State discussed above) and returns to the Sleep State when
the access point indicates EOSP in a downlink data or null frame
addressed to the portable communication device 18.
[0087] At block 202, once the portable communication device 18
decides to transition from the Sleep State to the Active State, it
notifies the access point 14 by sending a signal (e.g., an uplink
trigger frame (UTF)) to the access point 14 through the WLAN
transceiver 150. Generally, the uplink trigger frame may include a
power-save (PS) bit set to active. Following such transmission, the
portable communication device 18 remains active so the access point
14 can send any buffered downlink frames afterward. At step 204, an
acknowledgement (ACK) is transmitted from the access point 14 to
the WLAN transceiver 150 in response to receiving the signal (e.g.,
the UTF). As shown in FIG. 5, the uplink trigger frame, which is a
WLAN data packet, may at least partly coincide with the Bluetooth
TX slot 52. The received ACK signal should coincide with the
Bluetooth RX slot 54. Between the WLAN packet exchanges, there is a
Short Inter-Frame Spacing (SIFS), e.g., SIFS=10 .mu.s in
802.11b.
[0088] With the knowledge of the uplink packet size and the uplink
data rate, the portable communication device 18 is able to
determine when to start sending the UTF such that the downlink ACK
will happen after the beginning of the Bluetooth RX slot. The
determination of when to start sending the UTF may take into
account any uncertainty in the contention window, i.e., on a
carrier sense, the determination should take into account the
random back-off number that is used. In addition, the portable
communication device 18 may also take into consideration the
average medium access delay observed in the past. If the UTF packet
has no payload (NULL frame--480 bits), it may be sent during the
Bluetooth TX slot 54 (i.e., starts later than the TX slot leading
edge). If the UTF packet has a payload (e.g. with VoIP data of
certain voice CODEC), the UTF packet may start earlier, even
earlier than the Bluetooth TX slot leading edge. The primary goal
is that the leading edge of the downlink WLAN ACK packet 204
closely aligns with the leading edge of the Bluetooth RX slot
54.
[0089] In general, the UTF conveys the following information to the
access point 14: 1) In the MAC header, set Duration Field 206 to
protect the uplink trigger transmission; and 2) in the quality of
service (QoS) Control field, set transmit opportunity (TXOP) 208,
as shown in FIG. 6. The maximum TXOP is determined by the uplink
ACK 210 and next UTF 212. The TXOP window shall end at:
MIN(t.sub.RX-SIFS-T.sub.UTF-T.sub.ACK-SIFS), (t.sub.RX-D.sub.TX)),
where t.sub.RX is the starting time of the next Bluetooth RX slot,
T.sub.ACK is the transmission time of the uplink ACK at the most
robust rate, T.sub.UTF is the duration of the UTF packet, and
D.sub.TX is the duration of the Bluetooth TX slot. Therefore, the
TXOP window ends at the smaller value of
(t.sub.RX-SIFS-T.sub.UTF-T.sub.ACK-SIFS) or
(t.sub.RX-D.sub.TX).
[0090] Upon receiving the UTF transmitted from the WLAN transceiver
150 of the portable communication device 18, the access point 14
generally performs the following tasks: 1) the access point
determines out how much time 214 it has for downlink traffic
exchange based on the AP Turn around Delay 216 and the TXOP. This
can be calculated using the following algorithm:
Traffic Exchange Duration=TXOP-Turnaround Delay-ACK Tx
Time-SIFS-Duration Field in the UTF
The access point 14 then selects the appropriate payload size
(fragment if necessary) and data rate based on the available
traffic exchange duration.
[0091] Aspects of the invention may be used for non-real time (best
effort) WLAN traffic. In addition, aspects of the invention can
also be used for VoIP traffic as it solves the QoS problems usually
encountered when the portable communication device 18 has VoIP data
being received from the AP 14 and a Bluetooth voice link to the
user's accessory 34 (e.g., a headset). Since VoIP is periodic and
symmetric, the terminal sends uplink VoIP packet in the UTF and
retrieves downlink VoIP packet from the AP using the scheme shown
in FIG. 6. A typical VoIP transaction is shown in FIG. 7. For 64
kb/s VoIP and the most robust data rate (e.g., 1 mbps), the WLAN
packet lengths are on the order of 1.8 ms. For lower rate speech
codecs and/or higher data rates, shorter packets will result.
[0092] FIG. 7 is identical to FIG. 6 except that the UTF 200
includes VoIP payload that is initiated prior to receiving the
leading edge of the TX time slot 52. The Duration Field 206 is set
to protect the uplink trigger mechanism. Aspects of the present
invention allow the portable communication device 18 to synchronize
WLAN traffic with Bluetooth traffic. In addition, by aligning the
TX and RX transitions in the Bluetooth and WLAN traffic, a maximum
window is created that allows undisturbed transmission and
reception. In addition, by signaling the proper TXOP to the access
point, WLAN reception coincides with Bluetooth reception or
inactive slots.
[0093] Aspects of the invention may also be used for coexistence
between WLAN and WWAN (e.g., IEEE 802.16e, IEEE 802.16m, 3GPP,
etc.), as illustrated in FIGS. 8 and 9. Referring to FIG. 8, an
exemplary time division duplex (TDD) frame 250 is illustrated. The
TDD frame 250 includes a downlink sub-frame 252 and an uplink
sub-frame 254. As used herein "downlink" refers to network traffic
from the base station (e.g., base station 39) to the portable
communication device and "uplink" refers to network traffic from
the portable communication device to the base station.
[0094] As shown in FIG. 8, a typical TDD frame 250 usually contains
downlink sub-frame 252, in which portable communication devices
receive information from a base station (e.g., base station 39),
and uplink sub-frame 254, in which the portable communication
devices transmit information to base station. The lengths of
downlink and uplink sub-frames are configured by a predefined
ratio. For instance, if the length of the TDD frame is 5 ms and the
downlink-to-uplink ratio is 70 to 30, the lengths of corresponding
downlink and uplink sub-frames will be 3.5 ms and 1.5 ms,
respectively.
[0095] A typical TDD frame 250 may further include some form of
control block 256, and one or more idle guard periods 260. It is
noted that additional frame components may be present but are not
illustrated for purposes of brevity.
[0096] The control block 256 is commonly positioned in the
beginning of a TDD frame. The control block (also commonly referred
to as MAP) informs the portable communication device whether there
is data or control signals addressed to it in the downlink
sub-frame and, if data is present, where (in the packet) the data
is located. In addition, the control block also informs the
portable communication device whether the portable communication
device gets grants to transmit data or control signals to the base
station and, if granted such rights, informs the device of which
uplink sub-frame it may transmit. The guard periods 260 are
provided as time gaps to give the transceiver time to switch
between receive and transmit functions.
[0097] Referring to FIG. 9, an exemplary timing sequence (also
referred to as method 300) for a WWAN TDD system and WLAN
coexistence is illustrated in accordance with aspects of the
present invention. FIG. 9 illustrates three exemplary TDD frames
(e.g., TDD Frame X, TDD Frame X+1, and TDD FRAME X+2). The
following assumptions are made with the respect to the TDD frames:
1) the frames are 5 ms in duration and have a ratio of 70% downlink
and 30% uplink (such that the downlink duration is 3.5 ms and the
uplink duration is 1.5 ms). The guard periods are not shown. In
addition, the portable communication device receives and transmits
in every frame (i.e., the portable communication device is not
operating in sleep mode).
[0098] Referring to FIG. 9, at block 302, the portable
communication device 18 transmits a signal (e.g., an uplink trigger
frame (UTF)) to the access point 14 through the WLAN transceiver
150. At step 304, an acknowledgement (ACK) is transmitted from the
access point 14 to the WLAN transceiver 150 in response to
receiving the signal (e.g., the UTF). As shown in FIG. 10, the
uplink trigger frame (e.g. signal 302), which is WLAN data packet,
may at least partly coincide with the uplink portion of the TDD
Frame X (as shown in FIG. 9) (where X is a nominal TDD frame from
which to designate future TDD frames). The received ACK signal
should coincide with the beginning of the next TDD frame (e.g., TDD
frame X+1, as shown in FIG. 9). Between the WLAN packet exchanges,
there is a Short Inter-Frame Spacing (SIFS), e.g., SIFS=10 .mu.s in
802.11b.
[0099] With the knowledge of the uplink packet size and the uplink
data rate, the portable communication device 18 is able to
determine when to start sending the UTF such that the downlink ACK
will happen after the beginning of the TDD frame, within the
down-link portion of the next sub-frame (e.g., TDD frame X+1). The
determination of when to start sending the UTF may take into
account any uncertainty in the contention window, i.e., on a
carrier sense, the determination should take into account the
random back-off number that is used. In addition, the portable
communication device 18 may also take into consideration the
average medium access delay observed in the past. The primary goal
of such transmission is that the leading edge of the downlink WLAN
ACK packet 304 closely aligns with the leading edge of the downlink
sub-frame of next TDD frame.
[0100] In general, the UTF conveys the following information to the
access point 14: 1) In the MAC header, set Duration Field 306 to
protect the uplink trigger transmission; and 2) in the quality of
service (QoS) Control field, set transmit opportunity (TXOP) 308,
as shown in FIG. 9. The maximum TXOP is determined by the next
uplink ACK 310 and next UTF 312. The TXOP window shall end at:
MIN(t.sub.RX-SIFS-T.sub.UTF-T.sub.ACK-SIFS), (t.sub.RX-D.sub.TX)),
where t.sub.RX is the starting time of the next downlink sub-frame,
T.sub.ACK is the transmission time of the uplink ACK at the most
robust rate, T.sub.UTF is the duration of the UTF packet, and
D.sub.TX is the duration of the TDD uplink sub-frame.
[0101] Upon receiving the UTF transmitted from the WLAN transceiver
150 of the portable communication device 18, the access point 14
generally performs the following tasks: 1) the access point
determines out how much time 314 it has for downlink traffic
exchange based on the AP Turn around Delay 16 and the TXOP 308.
This can be calculated using the following algorithm:
Traffic Exchange Duration=TXOP-Turnaround Delay-ACK
Time-SIFS-Duration Field in the UTF
[0102] The access point 14 then selects the appropriate payload
size (fragment if necessary) and data rate based on the available
traffic exchange duration.
[0103] The coexistence functionality described herein may be a
computer program stored in the portable communication device. The
computer program may be downloaded from a network and/or installed
from CD and/or DVD and installed in memory 116. The processing
device 114 executes code the computer program in order to carry out
the functionality described with respect to FIGS. 3-9. For example,
the control circuit 112 is generally coupled to the first
transceiver 150 and the second transceiver 140, 155 wherein the
controller coordinates transmission and reception of the first
transceiver and the second transceiver by limiting transmission of
information from the associated access point to the first wireless
transceiver to time slots or sub-frames associated with the second
wireless transceiver in which the second transceiver does not
transmit.
[0104] Computer program elements of the invention may be embodied
in hardware and/or in software (including firmware, resident
software, micro-code, etc.). The invention may take the form of a
computer program product, which can be embodied by a
computer-usable or computer-readable storage medium having
computer-usable or computer-readable program instructions, "code"
or a "computer program" embodied in the medium for use by or in
connection with the instruction execution system. In the context of
this document, a computer-usable or computer-readable medium may be
any medium that can contain, store, communicate, propagate, or
transport the program for use by or in connection with the
instruction execution system, apparatus, or device. The
computer-usable or computer-readable medium may be, for example but
not limited to, an electronic, magnetic, optical, electromagnetic,
infrared, or semiconductor system, apparatus, device, or
propagation medium such as the Internet. Note that the
computer-usable or computer-readable medium could even be paper or
another suitable medium upon which the program is printed, as the
program can be electronically captured, via, for instance, optical
scanning of the paper or other medium, then compiled, interpreted,
or otherwise processed in a suitable manner. The computer program
product and any software and hardware described herein form the
various means for carrying out the functions of the invention in
the example embodiments.
[0105] Specific embodiments of an invention are disclosed herein.
One of ordinary skill in the art will readily recognize that the
invention may have other applications in other environments. In
fact, many embodiments and implementations are possible. The
following claims are in no way intended to limit the scope of the
present invention to the specific embodiments described above. In
addition, any recitation of "means for" is intended to evoke a
means-plus-function reading of an element and a claim, whereas, any
elements that do not specifically use the recitation "means for",
are not intended to be read as means-plus-function elements, even
if the claim otherwise includes the word "means". It should also be
noted that although the specification lists method steps occurring
in a particular order, these steps may be executed in any order, or
at the same time.
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